Current products requiring high intensity uniform illumination over the spectral range including ultraviolet (UV) to mid infrared (MIR) are based primarily on mercury arc lamps, which are expensive, inefficient, contain toxic materials dangerous to the environment, short lived, and operated by costly and high voltage ballasts. Xenon and metal halide short arc lamps have also been used, as have tungsten halogen sources.
As with mercury arc lamps, both xenon and metal halide lamps also contain toxic materials, expensive power supplies and ballasts and suffer from short lifetimes, requiring frequent replacement, interruptions in progress, and additional costs associated with both the labor for replacement and the lamp itself. A further disadvantage of tungsten halogen based systems is the relatively low output particularly for short blue and UV wavelengths.
The industry standard in both medical and industrial markets for providing high flux in the UVA band (extending from about 315 to 400 nm) optical radiation has been the mercury arc lamp. Mercury arc lamps are characterized by relatively narrow line spectra which in the UVA region is dominated by the i-line centered near 365 nm. Now, the fact that there are many mercury lines excited simultaneously between the deep UV and through the visible spectrum, means that much of the energy used to power the lamp is not going into this UV band which must be selected by using interference filters to extinguish the unwanted spectral components. Additional issues with the use of these high power mercury, xenon, and metal halide arc lamps include the undesirable affect of the arc moving around with time, resulting in flicker or instability in the intensity. Further, the fact that the arc moves requires an optical system with an effectively larger input aperture which reduces the maximum obtainable power density down stream in the optical system. Additionally, very large voltages are required from power supply ballasts on the order of kilovolts to start the lamps. These high voltages can damage sensitive medical and industrial instrumentation due to the emitted electromagnetic pulse. In addition to these issues with the use of mercury, xenon, and metal halide lamps, recent concern over the use of highly toxic materials has fueled the search for alternatives to the arc lamps and improvements over the low output and poor lifetime of tungsten based lamps.
It is a principle object of the present invention to provide an LED based projector system that replaces expensive toxic mercury based lamps where the LED based system is from 200% to 500% more efficient and >10× the lifetime relative to mercury lamps.
It is another object of the present invention to provide an LED based illumination system that operates at low voltage with no need for expensive and dangerous voltages required for the mercury based systems.
It is yet another object of the present invention to provide an LED based “Chip-on-Board” (COB) high power, high density LED die arrays in combination with unique non-imaging collection and imaging relay optics to provide a new generation of UV, Visible, and Mid Infrared LED projection systems as alternatives to toxic, short lived and energy inefficient mercury, xenon, metal halide and tungsten halogen lamp systems.
It is yet another object of the present invention to provide an LED projector that combines a very low thermal impedance “Chip-on-Board” (COB) LED die attachment technology with thermal impedance well under 1° C./W which is several times lower than conventional high performance high power LED prepackaged emitters. The use of such a low thermal impedance technology allows the current density to be increased substantially resulting in much higher optical power density and lower junction temperatures which translates into longer LED die lifetimes. Additionally, the warm up time for mercury, xenon and metal halide lamp systems is relatively long and they can not be pulsed on an off effectively. The much faster response time of LEDs allows a further reduction in energy usage as the LED based systems can be switched on and off where the arc lamp systems generally need to be operated continuously and switched on and off by use of mechanical shutters. Thus, the effective energy usage is even higher in practice for LEDs, depending on the duty cycle of the particular process in question.
Other objects of the invention will, in part, be obvious and, in part, appear hererinafter when the following detailed description is read in connection with the accompanying drawings.